Add unstable-static-encoding-str feature

Author: madsmtm

objc2-encode/Cargo.toml

@@ -18,5 +18,9 @@ repository = "https://github.com/madsmtm/objc2"
 documentation = "https://docs.rs/objc2-encode/"
 license = "MIT"
 
+[features]
+# Requires the `generic_const_exprs` feature
+unstable-static-encoding-str = []
+
 [package.metadata.docs.rs]
 default-target = "x86_64-apple-darwin"

objc2-encode/src/lib.rs

@@ -92,6 +92,8 @@
 #![deny(unsafe_op_in_unsafe_fn)]
 // Update in Cargo.toml as well.
 #![doc(html_root_url = "https://docs.rs/objc2-encode/2.0.0-beta.2")]
+#![cfg_attr(feature = "unstable-static-encoding-str", allow(incomplete_features))]
+#![cfg_attr(feature = "unstable-static-encoding-str", feature(generic_const_exprs))]
 
 #[cfg(doctest)]
 #[doc = include_str!("../README.md")]
@@ -108,8 +110,10 @@ mod encoding;
 mod parse;
 
 // Will be used at some point when generic constants are available
-#[allow(dead_code)]
+#[cfg_attr(not(feature = "unstable-static-encoding-str"), allow(dead_code))]
 mod static_str;
 
 pub use self::encode::{Encode, EncodeArguments, RefEncode};
 pub use self::encoding::Encoding;
+#[cfg(feature = "unstable-static-encoding-str")]
+pub use self::static_str::EncodingHelper;

objc2-encode/src/static_str.rs

@@ -1,3 +1,5 @@
+#[cfg(feature = "unstable-static-encoding-str")]
+use super::Encode;
 use super::Encoding;
 
 pub(crate) const fn static_int_str_len(mut n: u128) -> usize {
@@ -41,8 +43,7 @@ pub(crate) const fn static_encoding_str_len(encoding: Encoding<'_>) -> usize {
 
     match encoding {
         Char | Short | Int | Long | LongLong | UChar | UShort | UInt | ULong | ULongLong
-        | Float | Double | LongDouble | Bool | Void | String | Object | Class | Sel
-        | Unknown => 1,
+        | Float | Double | LongDouble | Bool | Void | String | Object | Class | Sel | Unknown => 1,
         Block | FloatComplex | DoubleComplex | LongDoubleComplex => 2,
         BitField(b, _type) => 1 + static_int_str_len(b as u128),
         Pointer(&t) => 1 + static_encoding_str_len(t),
@@ -61,7 +62,9 @@ pub(crate) const fn static_encoding_str_len(encoding: Encoding<'_>) -> usize {
     }
 }
 
-pub(crate) const fn static_encoding_str_array<const LEN: usize>(encoding: Encoding<'_>) -> [u8; LEN] {
+pub(crate) const fn static_encoding_str_array<const LEN: usize>(
+    encoding: Encoding<'_>,
+) -> [u8; LEN] {
     use Encoding::*;
 
     let mut res: [u8; LEN] = [0; LEN];
@@ -204,6 +207,38 @@ pub(crate) const fn static_encoding_str_array<const LEN: usize>(encoding: Encodi
     res
 }
 
+/// Workaround since we can't specify the correct `where` bound on `Encode`.
+#[cfg(feature = "unstable-static-encoding-str")]
+pub struct EncodingHelper<T>(T);
+
+#[cfg(feature = "unstable-static-encoding-str")]
+impl<T: super::Encode> EncodingHelper<T>
+where
+    [u8; static_encoding_str_len(T::ENCODING) + 1]: Sized,
+{
+    #[doc(hidden)]
+    // Contains null byte at the end
+    const __ENCODING_CSTR_BYTES: [u8; static_encoding_str_len(T::ENCODING) + 1] =
+        static_encoding_str_array(T::ENCODING);
+
+    /// TODO
+    pub const ENCODING_CSTR: *const u8 = Self::__ENCODING_CSTR_BYTES.as_ptr();
+}
+
+#[cfg(feature = "unstable-static-encoding-str")]
+impl<T: Encode> EncodingHelper<T>
+where
+    [u8; static_encoding_str_len(T::ENCODING)]: Sized,
+{
+    #[doc(hidden)]
+    const __ENCODING_STR_BYTES: [u8; static_encoding_str_len(T::ENCODING)] =
+        static_encoding_str_array(T::ENCODING);
+
+    /// TODO
+    pub const ENCODING_STR: &'static str =
+        unsafe { core::mem::transmute::<&[u8], &str>(&Self::__ENCODING_STR_BYTES) };
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;